By using the fMRI-adaptation technique, recent studies have demonstrated that the face specific region of fusiform face area (FFA) and the superior temporal sulcus (STS) show the adaptation effect for facial identity; a reduced activation to repeated presentation of identical face compared to presentation of different facial images (e.g., Andrews & Ewbank, 2004). In the present study, we used NIRS to examined whether a similar facial identity adaptation effects are shown in infants. By using Near-infrared spectroscopy (NIRS), we compared the hemodynamic responses of infants during the presentation of an identical face and the presentation of different faces. Based on our previous studies investigating face-related neural activation to faces by using NIRS (Otsuka et al., 2007; Nakato et al., 2009; Honda et al., 2009), we focused on the bilateral temporal regions. We hypothesized that infants would show the decreased brain activity during the repeated presentation of the same face compared to the presentation of the different faces. The responses were compared to the activation in the baseline period in which we presented various images of vegetables. The results were as follows: (1) the infants' brain activities in the channels surrounding the T5 and T6 regions increased during the observation of different faces compared to the baseline, suggesting that brain activity in infants' STS can be measured, (2) the repeated presentation of identical face lead to a significant reduction in the oxy-Hb concentrations compared to the presentation of different faces. These results suggested that the infants' STS showed the adaptation effect for facial identity. Our findings are consistent with the previous fMRI studies showing the adaptation effect in face recognition in adults' STS.

This research was supported by PRESTO (Japan Science and Technology Agency), a Grant-in-Aid for Scientific Research (18300090) from Japan Society for the Promotion of Science and a Grant-in-Aid for Scientific Research on Innovative Areas, “Face perception and recognition” (20119002), and “Development of biomarker candidates for social behavior” carried out under Strategic Research Program for Brain Sciences, by the Ministry of Education, Culture, Sports, Science and Technology. We are grateful to Prof. Norihiro Sadato, National Institute for Physiological Sciences, for his technical assistance. We also thank Yuko Hibi, Aki Tsuruhara, Midori Takashima, Jaile Yang, Yuka Yamazaki for their help in data collection.